U.S. patent number 5,306,235 [Application Number 07/954,176] was granted by the patent office on 1994-04-26 for failsafe iontophoresis drug delivery system.
This patent grant is currently assigned to Becton Dickinson and Company. Invention is credited to John L. Haynes.
United States Patent |
5,306,235 |
Haynes |
April 26, 1994 |
Failsafe iontophoresis drug delivery system
Abstract
An iontophoresis system includes an iontophoretic drug delivery
device for placement against the skin of a patient and having a
pair of electrodes, and a circuit for delivering and controlling
the current and voltage provided to the electrodes. The current and
voltage controlling circuit includes a power supply for generating
a voltage or current, an intermediary storage device and a first
switching circuit interposed and coupled to the power supply and
the intermediary storage device. The intermediary storage device is
selectively coupled to the drug delivery device through a second
switching circuit or device. Energy from the power supply is
transferred and stored in the intermediary storage device for later
delivery to the transdermal drug delivery device. In this way,
should a component of the circuit fail, the energy or power
delivered to the drug delivery device is interrupted or maintained
at least equal to a predetermined safe level to avoid damage or
injury to the patient's skin.
Inventors: |
Haynes; John L. (Chapel Hill,
NC) |
Assignee: |
Becton Dickinson and Company
(Franklin Lakes, NJ)
|
Family
ID: |
25495043 |
Appl.
No.: |
07/954,176 |
Filed: |
September 30, 1992 |
Current U.S.
Class: |
604/20;
607/149 |
Current CPC
Class: |
A61N
1/30 (20130101) |
Current International
Class: |
A61N
1/30 (20060101); A61N 001/30 () |
Field of
Search: |
;128/798,802,803,898
;604/70,49 ;607/149,151 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Application notes of Maxim Company, pp. 1-19 to 1-20,
undated..
|
Primary Examiner: Rosenbaum; C. Fred
Assistant Examiner: Rafa; Michael
Attorney, Agent or Firm: Hoffmann & Baron
Claims
What is claimed is:
1. An iontophoresis system, which comprises:
an iontophoretic drug delivery device for placement against the
skin of a patient, the drug delivery device including:
a first electrode;
means for holding an electrolyte situated in relation to the first
electrode such that an electrolyte held by the electrolyte holding
means is in electrical communication with the first electrode;
a second electrode; and
means for holding an ionic medication situated in relation to the
second electrode such that an ionic medication held by the
medication holding means is in electrical communication with the
second electrode; and
a circuit for controlling the current or voltage provided to the
electrodes of the drug delivery device, the circuit including:
first switching means, the first switching means being coupled to a
source of power, the first switching means having a conductive
state and a non-conductive state;
control means coupled to the first switching means for causing the
first switching means to be in one of the conductive state and the
non-conductive state;
an intermediary storage device, the intermediary storage device
being coupled to the first switching means such that energy from
the power source is transferred to and stored in the intermediary
storage device when the first switching means is in the conductive
state; and
second switching means, the second switching means being coupled
between the intermediary storage device and the electrodes of the
drug delivery device, the second switching means selectively
coupling the intermediary storage device to the drug delivery
device wherein when the first switching means is in the conductive
state, the second switching means effectively decouples the
intermediary storage device from the electrodes of the drug
delivery device and wherein when the first switching means is in
the non-conductive state, the second switching means effectively
couples the intermediary storage device to the electrodes of the
drug delivery device allowing energy stored in the intermediary
storage device to be transferred to the drug delivery device
thereby providing sufficient power to cause the ionic medication to
be driven into the skin of a patient.
2. An iontophoresis system as defined by claim 1, wherein the
intermediary storage device includes an inductor, and the second
switching means includes a diode.
3. An iontophoresis system having an iontophoretic drug delivery
device for placement against the skin of a patient, which
comprises:
a power source for generating a current and voltage; and
a circuit coupled between the power source and the drug delivery
device for delivering current and voltage form the power source to
the drug delivery device, the circuit including a plurality of
components; and
means for one of interrupting the power or maintaining the power at
least equal to a predetermined level if one of the power source or
circuit components fail to one of an open circuit and a short
circuit, thereby effectively preventing burns, shocks, and other
dangerous effects caused by excessive current and voltage being
applied to the skin of a patient.
4. A circuit for use in an iontophoresis system having an
iontophoretic drug delivery device for placement against the skin
of a patient, the iontophoretic drug delivery device having a
positive electrode and a negative electrode and the iontophoresis
system including a power source for generating a current and
voltage, the circuit comprising:
first switching means, the first switching means being coupled to
the power source of the iontophoresis system, the first switching
means having a conductive state and a non-conductive state;
control means coupled to the first switching means for causing the
first switching means to be in one of the conductive state and the
non-conductive state;
an inductor, the inductor being coupled to the first switching
means such that energy from the power source is transferred to and
stored in the inductor when the first switching means is in the
conductive state; and
a diode, the diode being coupled between the inductor and at least
one of the electrodes of the iontophoretic drug delivery device,
the diode selectively coupling the inductor to the at least one
electrode of the drug delivery device, wherein when the first
switching means is in the conductive state, the diode effectively
decouples the inductor from the electrodes and, wherein when the
first switching means is in the non-conductive state, the diode
effectively couples the inductor to the electrodes to allow energy
stored in the inductor to be transferred to the drug delivery
device thereby providing sufficient power to cause an ionic
medication to be driven into the skin of the patient.
5. A circuit as defined by claim 4, which further includes a
capacitor, the capacitor being electrically coupled to the diode
and further being coupled across the electrodes of the drug
delivery device for filtering voltage ripple and voltage transients
produced during the transfer of energy from the inductor to the
electrodes of the drug delivery device.
6. A circuit for use in an iontophoresis system having an
iontophoretic drug delivery device for placement against the skin
of a patient, the iontophoretic drug delivery device having a
positive electrode and a negative electrode and the iontophoresis
system including a power source for generating a current and
voltage, the circuit comprising:
a storage device, the storage device being coupled to the power
source to allow energy from the power source to be stored
therein;
first switching mans, the first switching means being coupled to
the storage device and the power source to define with the power
source and the storage device a current flow circuit for
transferring energy from the power source to the storage device,
the first switching means having a conductive state and a
non-conductive state;
control means coupled to the first switching means for causing the
first switching means to be in one of the conductive state and the
non-conductive state; and
second switching means, the second switching means being coupled to
the first switching means and the storage device and at least one
of the electrodes of the drug delivery device, the second switching
means selectively coupling the storage device to one of the
positive and negative electrode of the drug delivery device,
wherein energy is transferred to and stored in the storage device
from the power source when the first switching means is in the
conductive state, and wherein the second switching means
effectively decouples the storage device from the electrodes of the
drug delivery device when the first switching means is in the
conductive state; and wherein the second switching means
effectively couples the storage device to the electrodes of the
drug delivery device when the first switching means is in the
non-conductive state thereby allowing energy stored in the storage
device to be transferred to one of the positive and negative
electrodes of the drug delivery device to cause an ionic medication
to be driven into the skin of a patient.
7. A circuit as defined by claim 6, wherein the storage device
includes an inductor, and the second switching means includes a
diode.
8. A circuit for use in an iontophoresis system having an
iontophoretic drug delivery device for placement against the skin
of a patient, the iontophoresis drug delivery device having a
positive electrode and a negative electrode and the iontophoresis
system including a power source for generating a current and
voltage, the circuit comprising:
first switching means, the first switching means being coupled to
the power source, the first switching means having a conductive
state and a non-conductive state;
control means coupled to the first switching means for causing the
first switching means to be in one of the conductive state and the
non-conductive state;
a first inductor, the first inductor being coupled to the first
switching means such that energy from the power source is
transferred to and stored in the first inductor when the first
switching means is in the conductive state; and
a first diode, the first diode having an anode end and a cathode
end, the cathode end of the first diode being coupled to the first
inductor;
a filtering section, the filtering section being coupled between
the anode end of the first diode and to at least one of the
electrodes of the drug delivery device, the first diode selectively
coupling the first inductor to at least one electrode of the
iontophoretic drug delivery device through the filtering section,
wherein when the first switching means is in the conductive state,
the diode effectively decouples the inductor from the electrodes
and, wherein when the first switching means is in the
non-conductive state, the diode effectively couples the inductor to
the electrodes to allow energy stored in the first inductor to be
transferred to the iontophoretic drug delivery device thereby
providing sufficient power to cause an ionic medication to be
driven into the skin of a patient.
9. A circuit as defined by claim 8, which further comprises a
second diode, the second diode having an anode end and a cathode
end, the anode end of the second diode being coupled to the anode
end of the first diode.
10. A circuit as defined by claim 8, which further comprises a
zener-regulator diode, the zener-regulator diode having an anode
end and a cathode end, the anode end of the zener-regulator diode
being coupled to the negative electrode and the cathode end of the
zener-regulator diode being coupled to the positive electrode of
the drug delivery device.
11. A circuit as defined by claim 8, wherein the filtering section
is formed as a .pi. filter and includes an first capacitor having a
first end coupled to the anode of the first diode and a second end
coupled to the positive electrode, a second inductor having first
and second ends, the first end of the second inductor being coupled
to the anode of the first diode and the second end of the second
inductor being coupled to the negative electrode of the drug
delivery device, and a second capacitor coupled across the positive
and negative electrodes of the drug delivery device.
12. A circuit for use in an iontophoresis system having an
iontophoretic drug delivery device for placement against the skin
of a patient, the iontophoresis drug delivery device having a
positive electrode and a negative electrode and the iontophoresis
system including a power source for generating a current and
voltage, the circuit comprising:
a storage device, the storage device being coupled to the power
source to allow energy from the power source to be stored
therein;
first switching means, the first switching means being coupled to
the storage device and the power source to define with the power
source and the storage device a current flow circuit for
transferring energy from the power source to the storage device,
the first switching means having a conductive state and a
non-conductive state;
control means coupled to the first switching means for causing the
first switching means to be in one of the conductive state and the
non-conductive state, wherein energy is transferred to and stored
in the storage device from the power source when the first
switching means is in the conductive state;
second switching means, the second switching means being coupled to
the first switching means and to the storage device;
a filter circuit, the filter circuit being coupled to the second
switching means, the second switching means selectively coupling
the storage device to one of the positive and negative electrode of
the drug delivery device through the filter circuit, wherein energy
is transferred to and stored in the storage device from the power
source when the first switching means is in the conductive state,
and wherein the second switching means effectively decouples the
storage device from the electrodes of the drug delivery device when
the first switching means is in the conductive state, and wherein
the second switching means effectively couples the storage device
to the electrodes of the drug delivery device when the first
switching means is in the non-conductive state thereby allowing
energy stored in the storage device to be transferred to one of the
positive and negative electrode of the drug delivery device to
cause an ionic medication to be driven into the skin of a
patient.
13. A circuit as defined by claim 12, wherein the storage device
includes an inductor, and the second switching means includes at
least a first diode.
14. A circuit as defined by claim 12, which further comprises a
voltage clamping circuit, the voltage clamping circuit being
electrically coupled to at least one of the electrodes.
15. A circuit as defined by claim 12, which further comprises a
voltage regulating circuit, the voltage regulating circuit being
coupled across the positive and negative electrodes of the drug
delivery device.
16. A method for delivering and controlling energy provided to an
iontophoretic drug delivery device, the drug delivery device
including a power source, a storage device coupled to the power
source and a pair of electrodes on the drug delivery device coupled
to the storage device, the method comprising the steps of:
coupling the power source to the storage device, said storage
device being uncoupled from said electrodes while said power source
and storage device are coupled thereby permitting the transfer of
energy from the power source to the storage device; and
uncoupling the power source from the storage device, said storage
device being coupled to said electrodes while said power source and
storage device are uncoupled, said storage device thereby providing
energy to the iontophoretic drug delivery device to drive ionic
medication into the skin of a patient.
17. A method as defined by claim 16, which further comprises the
step of:
filtering the energy transferred from the storage device to the
electrodes of the drug delivery device thereby reducing voltage
ripple and transients.
18. A method for delivering and controlling energy provided to
power an iontophoretic drug delivery device having an ionic
medication thereon and a positive electrode and a negative
electrode, the iontophoresis system including a power source for
generating a current and voltage, the iontophoresis system further
including a circuit having: a storage device, the storage device
being coupled to the power source to allow energy from the power
source to be stored therein, first switching means, the first
switching means being coupled to the storage device, the first
switching means having a conductive state and a non-conductive
state, and second switching means, the second switching means being
coupled to the storage device and at least one of the electrodes of
the iontophoretic drug delivery device, the second switching means
having a conductive state and a non-conductive state, the method
comprising the steps of:
switching the first switching means into said conductive state
thereby transferring energy from the power source to the storage
device while said second switching means is effectively in the
non-conductive state; and
switching the first switching means into said non-conductive state
thereby disconnecting the power source from the storage device
while said second switching means is effectively in the conductive
state thereby transferring energy from the storage device to the
electrodes of the iontophoretic drug delivery device thus driving
the ionic medication into a patient's skin.
19. A method as defined by claim 8, which further comprises the
step of:
filtering the energy transferred from the storage device to the at
least one of the electrodes of the iontophoretic drug delivery
device thereby reducing voltage ripple and transients.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to iontophoretic devices for
delivering a drug or medicant to a patient transdermally, i.e.,
through the patient's skin, and more specifically relates to an
iontophoresis drug delivery system and circuit therefor which
limits the current or voltage provided to the patient's skin to a
safe level should a component of the circuit fail.
2. Description of the Prior Art
Iontophoresis can be defined as the electrically driven application
of drugs or medicants, in their ionic form, to the surface tissues
of a patient. The application of electric current causes migration
of ions into the tissue wherein such migration is proportional to
the quantity of current applied through the iontophoretic
system.
One of the major drawbacks of iontophoresis is skin irritation or
burns which can occur due to high current levels. It is known that
the impedance of a patient's skin can range from over 100,000 ohms
to nearly 1,000 ohms, depending on the duration that the
iontophoretic current is applied, the magnitude of the current
which is being delivered, the location of the system on the
patient's body, and other factors. In a system where the desired
current level, which is determined in part by the drug administered
to the patient, is 1 milliamp, a voltage potential of 100 volts
would result if the skin impedance is 100,000 ohms. Such a voltage
would cause undesirable sensations to the user.
Numerous attempts have been made to control the amount of current
or voltage provided to a patient during iontophoresis. For example,
U.S. Pat. No. 4,292,968 to Ellis discloses an apparatus for
delivering constant current during ion therapy (iontophoresis)
which will abruptly switch to delivering constant voltage when the
voltage across the electrodes of the drug delivery device reaches a
predetermined level. The circuit disclosed in the Ellis patent
includes a voltage limiter 14 which is provided in shunt with the
electrodes of the device for limiting the output voltage across the
electrodes. The Ellis patent describes the voltage limiter 14 as
functioning as a variable resistive path shunting the electrodes.
When the electrode voltage is less than a predetermined voltage,
the limiter 14 is stated to present a high resistance and all the
current generated by the circuit is provided to the electrodes.
However, when the voltage across the electrodes reaches the
predetermined voltage, the resistance of the limiter 14 is stated
to drop, drawing current that would have been provided to the
electrodes.
One of the major disadvantages of the circuit described in the
Ellis patent is that it is not failsafe. Should certain of the
components of the circuit fail, it is possible for the Ellis
circuit to deliver excessive current to the patient, causing skin
irritation or tissue damage. For example, if the voltage limiter 14
failed such that it no longer acted as a variable resistor or no
longer shunted the electrodes of the device, no voltage regulation
would occur when the predetermined voltage across the electrodes is
reached. The voltage across the electrodes could reach dangerous
levels, resulting in skin burns or tissue damage.
Another iontophoresis device is disclosed in U.S. Pat. No.
4,141,359 to Jacobsen, et al. The Jacobsen, et al. patent discloses
an epidermal iontophoresis device which is stated to be capable of
maintaining a constant current through the epidermal tissue. To
prevent excessive voltage build-up and the accompanying dangers of
shock and burns, a comparator circuit monitors current flow and
voltage across the electrodes of the device and automatically
triggers an SCR shut down circuit when impedance readings are
outside of predetermined limits.
As with the circuit disclosed in the Ellis patent, the
iontophoresis device described in the Jacobsen, et al. patent is
not safe if certain components fail. For example, if the SCR fails
and becomes effectively an open circuit, it will no longer be
capable of de-energizing the current source used in the circuit,
resulting in burns, shocks and other dangerous effects of excessive
current and voltage.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide an
iontophoresis system having failsafe capability to prevent
excessive current or voltage from being provided to a patient
during transdermal drug delivery should a component of the system
fail.
It is another object of the present invention to provide an
iontophoresis drug delivery system which has an inherent power
limitation which limits the power delivered to a patient undergoing
transdermal drug delivery.
It is yet another object of the present invention to provide a
circuit for use in an iontophoresis system and for connection to a
transdermal drug delivery device, which circuit is inherently power
limiting and/or failsafe such that, if certain components of the
circuit fail, no excessive current or voltage is provided to the
patient undergoing iontophoresis.
It is a further object of the present invention to provide an
iontophoresis system and method which overcomes the inherent
disadvantages of known systems and methods.
In accordance with one form of the present invention, a failsafe
iontophoresis drug delivery system includes an iontophoretic drug
delivery device for placement against the skin of a patient, and a
failsafe circuit for controlling current or voltage provided to the
drug delivery device. More specifically, the iontophoretic drug
delivery device of the system includes a first electrode, which may
act as a cathode, and a container or other structure for holding an
electrolyte situated in relation to the first electrode such that
the electrolyte is in electrical communication with the first
electrode. The drug delivery device also includes a second
electrode, which may act as an anode, and a container or other
structure for holding an ionic medication situated in relation to
the second electrode such that the medication is in electrical
communication with the second electrode.
The failsafe circuit for controlling current or voltage provided to
the first and second electrodes includes a power supply, for
example, a constant current source or a constant voltage source.
The circuit also includes an intermediary storage circuit or
device. The storage device is selectively coupled by way of a first
switching circuit or the like to the power supply. The intermediary
storage device is also selectively coupled, by a second switching
circuit, device or the like, to the electrodes of the drug delivery
device.
The intermediary storage circuit or device may be, for example, a
capacitor or inductor circuit, which is capable of storing energy
when connected to the power supply. A control circuit may be used
to open or close the first switching circuit, so that energy may be
transferred to and stored in the intermediary storage device, and
may be used to control the second switching circuit, if such is
included, to allow energy stored in the storage device to be
transferred to the drug delivery device.
The failsafe iontophoresis system and circuit of the present
invention only allows energy stored in the storage device to be
transferred to the electrodes of the transdermal drug delivery
device. The circuit will not allow the power supply to be connected
directly to the electrodes and, even more preferably, if one of the
components should fail in the circuit of the iontophoresis system,
the voltage or current provided to the electrodes will either be
zero or be limited to a predetermined safe voltage and current.
These and other objects, features and advantages of the present
invention will become apparent from the following detailed
description of illustrative embodiments thereof, which is to be
read in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an iontophoresis system formed in
accordance with one form of the present invention.
FIG. 2 is a cross-sectional view of a portion of the iontophoresis
system of the present invention shown in FIG. 1.
FIG. 3 is a schematic diagram of one form of an iontophoresis
system formed in accordance with the present invention and shown in
block diagram form in FIG. 1.
FIG. 4 is a schematic diagram of a second embodiment of an
iontophoresis system formed in accordance with the present
invention.
FIG. 5 is a schematic diagram of a third embodiment of an
iontophoresis system formed in accordance with the present
invention.
FIG. 6 is a graph plotting the ideal and measured output
voltage/current curves for the circuit shown in FIG. 5.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring initially to FIG. 1 of the drawings, it will be seen that
an iontophoresis system for delivering ionic medication to a
patient transdermally, that is, through the skin of the patient,
basically includes a transdermal drug delivery device 2 for
placement against the skin of the patient, and a circuit 4 for
controlling the current and voltage provided to the drug delivery
device.
One form of a transdermal drug delivery device 2 is illustrated by
FIG. 2. The transdermal drug delivery device basically includes a
first electrode 6, which may act as a cathode, and a second
electrode 8, which may act as an anode. The transdermal drug
delivery device 2 is placeable against the skin 10 of a patient so
that the anode electrode 8 and cathode electrode 6 are in
electrical communication with the patient's skin.
Adjacent to the anode (i.e., the second electrode 8) is a container
or other suitable structure 12 defining a well for holding an ionic
medication 14 in place between the anode and the skin of the
patient. Similarly, adjacent to the cathode (i.e., the first
electrode 6) is a container or other suitable structure 16 forming
a well for holding an electrolyte 18 in place between the cathode
and the skin of the patient.
When a voltage V.sub.a is impressed across the first and second
electrodes 6, 8, current I.sub.a will flow through the skin of the
patient, driving the ionic medication into the skin and tissue to
be absorbed by the patient's body.
Referring again to FIG. 1 of the drawings, the iontophoresis system
of the present invention also includes a current or voltage
delivery circuit 4 which controls the current passing through each
of the electrodes 6,8 and the voltage across the electrodes. The
current and voltage delivery circuit 4 basically includes a power
source or supply 20, which may be a constant current source or a
constant voltage source. The circuit also includes an intermediary
storage device or circuit 22. In one form of the present invention,
the intermediary storage device may be a capacitor or inductor
circuit, as will be described in greater detail. Energy from the
power source 20 will be transferred to and stored in the
intermediary storage device 22 for later delivery to the
transdermal drug delivery device 2.
The intermediary storage device 22 is selectively coupled to the
power source 20 through first switching means 24. The first
switching means 24, which is interposed between the power supply
and the intermediary storage device, may be in the form of an
electronic switch, field effect transistor (FET) or the like, to
selectively interrupt the connection between the power supply 20
and the intermediary storage device 22.
A control circuit 26 is coupled to the first switching means 24 and
is used to activate the first switching means to selectively open
and close the connection between the power supply 20 and the
intermediary storage device 22. The control circuit 26 may be any
one of a number of suitable circuits which may be used, such as an
astable multivibrator which provides an output control signal to
the first switching means 24 having a predetermined duty cycle and
frequency to control the operation of the first switching
means.
When the first switching means 24 is in one state (i.e., a
conductive state), the power supply output is coupled to the
intermediary storage device 22 so that energy generated by the
power supply 20 may be transferred to the intermediary storage
device and stored therein. When the first switching means 24 is in
a second state (i.e., a non-conductive state), the intermediary
storage device 22 is disconnected from the power supply 20 so that
no additional energy is stored in the intermediary storage device.
The quantity of energy transferred to and stored in the
intermediary storage device 22 may be controlled by the control
circuit 26 and the parameters of the current or voltage source
selected as the power supply 20.
The current and voltage delivery circuit 4 of the iontophoresis
system also includes second switching means 28. The second
switching means 28 is interposed between the output of the
intermediary storage device 22 and the transdermal drug delivery
device 2. The second switching means 28 has a conductive and a
non-conductive state. When the second switching means is in the
conductive state, the intermediary storage device 22 is effectively
coupled to the transdermal drug delivery device 2 so that energy
stored in the intermediary storage device may be transferred to the
drug delivery device. When the second switching means 28 is in the
non-conductive state, the intermediary storage device 22 is
effectively decoupled from the transdermal drug delivery device and
no energy is transferred.
In one form of the present invention, the second switching means 28
may be a switch circuit or the like, similar to the first switching
means, and controlled to become conductive or non-conductive by the
control circuit 26. The second switching means may also be a diode
circuit or the like, as will be described in greater detail.
The iontophoresis system of the present invention shown in FIG. 1
of the drawings operates in the following manner. Energy generated
by the power supply 20 is transferred to the intermediary storage
device 22 and stored therein when the control circuit 26 causes the
first switching means 24 to become conductive so that the power
supply is effectively coupled to the intermediary storage device.
During energy storage, the intermediary storage device is
effectively decoupled by the second switching means 28 from the
transdermal drug delivery device 2. The control circuit 26 then
causes the first switching means 24 to become non-conductive,
effectively decoupling the power supply 20 from the intermediary
storage device 22 so that no more energy is transferred to and
stored in the storage device. Accordingly, only a predetermined
amount of energy is stored in the intermediary storage device for
later transfer to the transdermal delivery device. The second
switching means 28 now becomes conductive, effectively coupling the
intermediary storage device 22 to the transdermal drug delivery
device 2 so that the energy or power stored in the storage device
may be transferred in the form of a voltage and current to the
electrodes 6, 8 of the transdermal drug delivery device, causing
the ionic medication to be driven into the skin and tissue to be
absorbed by the patient's body.
One of the advantages of having an intermediary storage device 22
positioned between the power supply 20 and the transdermal drug
delivery device 2 is that only a predetermined amount of energy is
transferred to the intermediary storage device. The power supply is
not normally directly coupled to the transdermal drug delivery
device and so, if a component fails, the voltage or current
provided to the electrodes 6, 8 of the drug delivery device will
decrease to zero or to a predetermined safe level so as not to
cause injury to the patient undergoing iontophoresis. There is no
normal direct connection between the power supply 20 and the drug
delivery device 2.
Only the predetermined amount of energy, stored in the storage
device 22, is provided to the electrodes of the transdermal drug
delivery device 2 in the form of a voltage or current. A power
supply would effectively have unlimited energy to transfer.
However, the intermediary storage device 22 only has a quantified
packet of energy to deliver to the drug delivery device and no
more. Accordingly, there is greater control of the power provided
to the drug delivery device connected to the patient in the event
of a failure, as only that energy stored in the intermediary
storage device or a predetermined safe level is delivered to the
transdermal drug delivery device 2.
A preferred form of the iontophoresis system of the present
invention is shown in FIG. 3 of the drawings. The current and
voltage delivery circuit 4 shown in FIG. 3 and which is connected
to the transdermal drug delivery device 2 is what is commonly
referred to as a buck-boost circuit.
The power supply 20 generates a voltage E which is provided across
an inductor L1, which acts as the intermediary storage device 22,
when an electronically controlled single pole, single throw switch
S1 (which acts as the first switching means 24) is activated to be
conductive by the control circuit 26. The energy from the power
supply 20 is transferred to and stored in the inductor L1.
A diode D1 is used as the second switching means 28. The diode D1
has its cathode connected to the inductor L1 on the positive side
of the power supply 20, and its anode connected to the negative
(cathode) electrode 6 of the transdermal drug delivery device. The
other end of the inductor L1 and the negative output of the power
supply are coupled to the positive (anode) electrode 8. While the
energy is being transferred from the power supply 20 to the
inductor L1, the diode D1 is back biased and no current or voltage
is provided to the electrodes of the transdermal drug delivery
device. After the energy has been transferred to the inductor, the
control circuit 26 causes switch S1 (i.e., the first switching
means 24) to open. The field induced by the voltage impressed
across the inductor L1 collapses, causing a current to flow and
forward biasing the diode D1. The forward biased diode allows a
current to flow through the electrodes 6, 8 and a voltage V to be
impressed across the electrodes of the transdermal drug delivery
device 2 until all or part of the energy which had been stored in
the inductor has been dissipated. After the inductor L1 has
discharged, current will cease flowing through the electrodes of
the drug delivery device.
In a preferred form of the buck-boost circuit shown in FIG. 3, a
capacitor C1 may be coupled in parallel with the positive and
negative electrodes 8, 6 of the transdermal drug delivery device 2.
The capacitor C1 serves the purpose of filtering ripple on the
output voltage V and to prevent voltage transients across the
electrodes of the drug delivery device.
The advantage of the iontophoresis system and circuit shown in FIG.
3 is that, if any component fails, no voltage or current or a
predetermined safe level of voltage or current will be delivered to
the electrodes of the transdermal drug delivery device. For
example, if the capacitor C1 should short, the voltage V across the
electrodes of the transdermal drug delivery device 2 will become
zero. If the capacitor C1 becomes an open circuit due to failure,
it will have no major effect on the circuit except for a loss of
filtering and the circuit will operate normally.
If the diode D1 fails and becomes an open circuit, the transdermal
drug delivery device 2 is disconnected from the inductor L1 and the
power supply. If the diode shorts, the output voltage V on the
electrodes will be effectively equal to the reverse of the power
supply voltage -E volts when the first switching means 24 (i.e.,
switch S1) closes, and will be equal to V volts when the first
switching means 24 opens and the inductor discharges. Accordingly,
the average voltage supplied to the electrodes will be at a
predetermined safe level between -E and V volts.
If the inductor L1 fails and appears as an open circuit, no current
and voltage is provided to the electrodes of the drug delivery
device 2, as current is blocked by the back biased diode D1. If the
inductor shorts, the voltage across the electrodes and the current
provided to the electrodes will become zero, as whatever charge
remains in the capacitor C1 will dissipate.
If the first switching means 24 (i.e., switch S1) should fail and
appear as a short circuit, no energy will be transferred to the
transdermal drug delivery device 2, as the inductor L1 appears as a
short circuit when fully charged. The current into the inductor
ramps up to its limit and the inductor remains charged, as it
cannot transfer its energy to the drug delivery device. Of course,
if the switch S1 fails as an open circuit, no voltage or current
will be delivered to the electrodes of the drug delivery
device.
FIG. 4 illustrates a second embodiment of the iontophoresis system
of the present invention. The circuit shown schematically in FIG. 4
is commonly known as a "boost" circuit or a "step-up converter." In
a boost circuit, the voltage E generated by the power supply 20 is
usually much less than the voltage V generated on the output of the
circuit and, in the present invention, provided to the electrodes
6, 8 of the transdermal drug delivery device. In effect, the
circuit increases or "boosts" the power supply voltage E to some
usable output voltage V. The output voltage of the power supply may
be relatively low and determined to be a safe level, and the output
voltage V provided to the electrodes of the transdermal drug
delivery device 2 may be at a higher level to drive the ionic
medication into the skin and tissue of the patient.
More specifically, the boost circuit of the iontophoresis system
includes an inductor L2 which is selectively coupled across the
outputs of the power supply 20 when the first switching means 24
(i.e., switch S2) is in the conductive state. Energy from the power
supply 20 is transferred to the inductor L2 when the first
switching means is conductive.
The circuit also includes a diode D2 which acts as the second
switching means 28. The diode D2 has its anode connected to the
junction of one pole of the switch S2 and the inductor L2, and its
cathode connected to the positive electrode 8 of the transdermal
drug delivery device 2. Also, a capacitor C2 for filtering out
ripple may be included and connected in parallel with the
electrodes 6, 8 of the drug delivery device, with the negative
electrode 6 also being connected to the other pole of the switch S2
and the negative output of the power supply 20.
After the inductor L2 has charged, the first switching means
(switch S2) is opened by the control circuit 26. The inductor
discharges through the diode D2 and transfers its energy to the
transdermal drug delivery device, driving the ionic medication into
the skin and tissue of the patient. Accordingly, only a packet of
energy which is stored in the inductor L2 is transferred to the
drug delivery device. It should be noted that the arrangement of
the components of the boost circuit shown in FIG. 4 is slightly
different from the block diagram illustrated by FIG. 1 in that the
position of the first switching means (i.e., switch S2) and
inductor L2 (i.e., the storage device 22) are reversed. However,
the circuits function similarly by causing power from the supply to
be transferred to and stored in the storage device and the stored
power is later transferred to the electrodes of the drug delivery
device.
Should a component fail in the circuit described above, the voltage
V provided to the electrodes of the transdermal drug delivery
device 2 will decrease to be less than or equal to the power supply
voltage E. The power supply voltage E is, as mentioned previously,
selected to be at a safe level which will prevent burns and damage
to the patient's skin.
More specifically, if the capacitor C2 fails and appears as an open
circuit, more voltage ripple will be present on the electrodes but
still only the energy stored in the inductor L2 will be delivered
to the transdermal drug delivery device. If the capacitor C2 fails
as a short circuit, the electrodes 6,8 of the drug delivery device
are shorted and no current flows through the patient's skin.
If the diode D2 fails as an open circuit, no current or voltage is
provided to the transdermal drug delivery device. If the diode
fails as a short circuit, the output voltage V on the electrodes
will be effectively O volts when the first switching means 24
(switch S2) closes, and equal to voltage V when the first switching
means opens and the inductor L2 discharges. Accordingly, the
average voltage supplied to the electrodes will be at a
predetermined safe level between voltages E and V.
If the first switching means 24 (i.e., switch S2) fails as an open
circuit, the inductor L2 will charge and effectively act as a short
circuit and the voltage V delivered to the drug delivery device
will substantially equal the safe power supply voltage E. If the
switch S2 fails as a short circuit, the diode D2 will never be
forward biased and the output voltage V provided to the electrodes
of the transdermal drug delivery device will be zero.
If the inductor L2 fails as an open circuit, no energy will be
transferred from the power supply 20 to the transdermal drug
delivery device 2. If the inductor fails as a short circuit, the
output voltage V across the electrodes of the transdermal drug
delivery device will be approximately equal to the average between
the power supply voltage E (when the first switching means opens)
and O volts (when the first switching means closes).
FIG. 5 illustrates a third embodiment of the iontophoresis system
of the present invention. The transdermal drug delivery device 2 is
connected to the current and voltage delivery circuit 4 as shown in
FIG. 5. The current and voltage delivery circuit 4 as shown in FIG.
5 is a buck-boost circuit similar to the buck-boost circuit shown
in FIG. 3 and as described above. However, the present embodiment
differs from that of FIG. 3 in that the circuit of FIG. 5 is
provided with additional ripple filtering means and output
protection means in view of the potential for malfunction of
circuit elements.
As shown in FIG. 5, an inductor L3 has a first end coupled to
switch S3 and a second end coupled to a node 32. A power supply 20
generates a voltage E which is provided across inductor L3. L3 acts
as the intermediary storage device 22 when an electronically
controlled single pole, single throw (SPST) switch S3 (which acts
as the first switching means 24) is activated to be conductive by
the control circuit 26. The energy provided by the power supply 20
is transferred to and stored in the inductor L3.
A diode D3 functions as the second switching means 28. The diode D3
has its cathode end connected to the inductor L3 on the positive
side of the power supply 20. The anode end of diode D3 is connected
to the anode end of a second diode D4 at a second node 30. Diode D4
will act as a short under certain conditions within the voltage
delivery circuit 4 in order to prevent node 30 from going positive.
More specifically, if diode D3 shorts, the circuit will try to
drive the negative electrode positive. Diode D4 effectively clamps
the negative electrode from going positive. This provides added
protection for the circuit. The cathode of diode D4 is coupled to
node 32.
Also coupled to node 30, which electrically connects the anodes of
diodes D3 and D4, is a first end of a capacitor C3 and a first end
of an inductor L4. The second end of inductor L4 is coupled to a
first end of a capacitor C4 at a third node 34, effectively forming
a .pi. filter section which removes most ripple or transients from
the signal provided to the transdermal drug delivery device 2. The
second end of capacitor C3 and the second end of capacitor C4 are
coupled to node 32. Also, a capacitor C5 having a capacitance that
is smaller in value than capacitor C4 but having a greater
frequency response is connected in parallel across capacitor C4. In
this manner, the .pi. filter section with capacitors C4 and C5
reduce any transients or ripple in the voltage supplied to the
electrodes of the drug delivery device.
A zener diode D5 having an anode end and a cathode end is connected
at its anode end to the negative (cathode) electrode 6 of the
transdermal drug delivery device 2 and to node 34, which also
connects inductor L4 and capacitors C4 and C5. The cathode end of
zener diode D5 is coupled to node 32. All of the above-identified
components connected to node 32 are coupled to the positive (anode)
electrode 8. The zener diode D5 ensures that the voltage provided
to the electrodes does not exceed a predetermined voltage
level.
The operation of the iontophoresis system shown in FIG. 5 will now
be described.
When the transdermal drug delivery device 2 is coupled to the
current and voltage delivery circuit 4 at electrodes 6, 8, switch
S3 is thrown by control circuit 26 and the energy is provided from
the power supply 20 to the inductor L3. The diode D3 is back biased
so that no current is provided to the rest of the circuit including
the filter section comprising capacitors C3, C4, C5 and inductor
L4, zener-regulator diode D5 or the electrodes of the transdermal
drug delivery device 2.
After the inductor has been energized, the control circuit 26
causes switch S3 (i.e., the first switching means 24) to open.
Thereafter, the field induced by the voltage impressed across the
inductor L3 collapses, causing a current to flow through inductor
L3 and forward biasing the diode D3. The forward biased diode D3
allows a current to flow through the .pi. filter section and
electrodes 6, 8. In addition, a voltage V is impressed across the
electrodes of the transdermal drug delivery device 2 until all or
part of the energy which had been stored in the inductor L3 has
been dissipated to the transdermal drug delivery device 2. After
the inductor L3 has discharged, current will cease flowing through
the electrodes 6, 8 of the drug delivery device. Thereafter, the
SPST switch S3 is periodically activated to connect the voltage
source 20 to inductor L3.
In addition to the advantages mentioned above with respect to the
embodiment depicted in FIG. 3, the advantage of the iontophoresis
system of the present embodiment is that if diode D3 malfunctions
and is shorted, the negative (cathode) electrode 6 of the
transdermal drug delivery device 2 will be prevented from going
positive. Also, the filtering section comprising capacitors C3, C4
and inductor L4 (which section is configured as a .pi. filter)
provides for a smoother DC output and therefore more efficient use
of the energy stored and released from the supply 20.
To facilitate an understanding of the invention, it should be noted
that in the embodiments described previously, the diodes are
considered ideal devices with no voltage drop. Also, for a 6 volt
power supply (i.e., E=6 volts), the preferred values of the
components shown in FIG. 5 are the following: inductor L3=390
.mu.H; inductor L4=82 .mu.H; capacitor C4=10 .mu.f; capacitor
C5=0.01 .mu.f; diode D5=16 volt zener diode; and diodes D3 and D4
are Part Nos. BAS40 manufactured by Siemens Components, Inc. in
Iselin, N.J.
FIG. 6 is a graph depicting an ideal voltage/current curve for a
constant 40 mW power provided to the transdermal drug delivery
system and the measured output voltage/current curve for the
circuit shown in FIG. 5. A constant power with the fail-safe
capabilities described previously is what is desired for the
iontophoresis system of the present invention, and the actual
constant power limitation, which closely follows the ideal curve,
is what is achieved using the circuit shown in FIG. 5. It should be
noted that a constant power provided to the electrodes of the
transdermal drug delivery device is achieved without feedback, that
is, without the need to monitor the voltage or current provided to
the electrodes.
As described in detail previously, the iontophoresis system of the
present invention is failsafe in that a controlled amount of
energy, in the form of a voltage or current, is provided to the
transdermal drug delivery device. Specifically, under normal
operation the power supply is not connected directly to the
transdermal drug delivery device 2. Therefore, if a failure occurs
in one of the components, only the controlled and predetermined
quantity of energy stored in the storage device, i.e., inductor L3,
used in the system is delivered to the transdermal drug delivery
device. Therefore, the voltage provided to the electrodes of the
transdermal drug delivery device decreases from an initial safe
level to a predetermined level so that damage or burns to the
patient's skin may be avoided.
Although illustrative embodiments of the present invention have
been described herein with reference to the accompanying drawings,
it is to be understood that the invention is not limited to those
precise embodiments, and that various other changes and
modifications may be effected therein by one skilled in the art
without departing from the scope or spirit of the invention.
* * * * *